﻿using System;
class PerimeterOfCircle
{
    static void Main()
    {
        int circleradius;
        double pi = Math.PI;
        Console.Write("Please input circle radius: ");
        while (true)
        {
            try
            {
                circleradius = int.Parse(Console.ReadLine());
                break;
            }
            catch (Exception ex)
            {
                Console.Write(ex.Message + "\nPlease re-enter first number:");
            }
        }
        Console.WriteLine("the perimeter of circle with r = {0}, is: {1:F4}", circleradius, (2*circleradius*pi));
        Console.ReadLine();
    }
}

